Messages in this thread | | | From | Linus Torvalds <> | Date | Tue, 23 Aug 2022 11:09:22 -0700 | Subject | Re: mainline build failure for loongarch allmodconfig with gcc-12 |
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On Tue, Aug 23, 2022 at 1:34 AM Sudip Mukherjee (Codethink) <sudipm.mukherjee@gmail.com> wrote: > > I have been trying to build loongarch as part of my nightly builds, and > I can build loongson3_defconfig without any error. But allmodconfig fails > with the error: > > In function '__cmpxchg', > inlined from 'ssh_seq_next' at drivers/platform/surface/aggregator/controller.c:61:9,
Looks like ssh_seq_next() wants to do an atomic cmpxchg() on a single byte value, and the Loongarch implementation only does 4- and 8-byte versions.
It looks like loongarch - from its MIPS heritage - inherited the "we can't do atomics on byte variables", so that it needs the same strange "do bytes as word accesses with mask-and-shifts".
For MIPS, the code is in __xchg_small() in arch/mips/kernel/cmpxchg.c.
Alpha has something similar, except it's all done in inline asm in arch/alpha/include/asm/xchg.h (look for "____cmpxchg(_u8," in there.
Of course, we could just add a Kconfig variable like "ARCH_LACKS_BYTE_ATOMICS" and make that driver depend on it not being true, and just have Loongarch set it.
But I think loongarch should just implement the byte masking stuff. Particularly since I suspect it can just copy the MIPS code as-is.
Linus
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